Encoder device for use with polydecade consumption or usage meters

ABSTRACT

The encoding wheels associated with successive decades of a polydecade meter are divided into sectors. The rotational positions of each of the said encoding wheels are determined by conventional reading means, which may for example, optically examine tracks of coding that are present around the periphery of a wheel. The sectors are read out in a cyclic Gray code, which is then converted for each decade to a decimal number corresponding to the sector. Ambiguity correction is effected by examining the higher decade in the case of any pair of adjacent decades, and using its value to establish a possible range of the lower decade wheel. The higher decade is defined as the slower moving wheel. The lower decade wheel is then examined to determine whether it falls in the determined range, and thereupon the read value of the coarse wheel (higher decade) is adjusted by plus or minus 1, or allowed to stand, in accordance with the measured lower decade or fine wheel value relative to the cited range. Means are further present, for evaluating the total number of accumulated sectors that have passed a reference point in the case of the lower decade or least significant digit (LSD) wheel, and for then scaling the sectors determined to be cumulatively present on each wheel to decimal values. For purposes of clarity the higher decade is also referred to as the coarse or slower moving wheel, while the lower decade is also called the fine, faster or least significant digit (LSD) wheel.

United States Patent 1 1 Beck Aug. 5, 1975 ENCODER DEVICE FOR USE WITHPOLYDECADE CONSUMPTION 0R USAGE METERS [75] Inventor: Donald C. Beck,Parsippany. NJ.

[73] Assignee: Automated Technology Corporation,

Hackensack. NJ.

[22] Filed: Jan. 18, 1974 [21] Appl. No.: 434,422

[52], U.S. Cl. 340/347 P; 340/347 AD [51] Int. Cl. G08c 9/00: H03k 13/00[58] Field of Search 340/347 P 56] References Cited UNITED STATESPATENTS 3.142.835 7/1964 Larky 340/347 3.262.108 7/1966 Schuman 340/3473,376,567 4/1968 Brothmun et al. 340/188 3.560.961 2/1971 Mueller340/347 [57] ABSTRACT The encoding wheels associated with successivedecades of a polydecade meter are divided into sectors.

The rotational positions of each of the said encoding wheels aredetermined by conventional reading means. which may for example,optically examine tracks of coding that are present around the peripheryof a wheel. The sectors are read out in a cyclic Gray code, which isthen converted for each decade to a decimal number corresponding to thesector. Ambiguity correction is effected by examining the higher decadein the case of any pair of adjacent decades, and using its value toestablish a possible range of the lower decade wheel. The higher decadeis defined as the slower moving wheel. The lower decade wheel is thenexamined to determine whether it falls in the determined range, andthereupon the read value of the coarse wheel (higher decade) is adjustedby plus or minus 1, or allowed to stand, in accordance with the measuredlower decade or fine wheel value relative to the cited range. Means arefurther present, for evaluating the total number of accumulated sectorsthat have passed a reference point in the case of the lower decade orleast significant digit (LSD) wheel, and for then scaling the sectorsdetermined to be cumulatively present on each wheel to decimal values.For purposes of clarity the higher decade is also referred to as thecoarse or slower moving wheel, while the lower decade is also called thefine, faster or least significant digit (LSD) wheel.

7 Claims, 2 Drawing Figures COARSE FINE DECADE z I011 DECADE 32 READOUTj J'g READOUT 3 2 l 3 2 I 0 22220 INCLUDED N2 222 SCALER 40 CORRECTION 1ANALYSIS LOGIC REVOLUTIONS CORRECTION 44f LOGIC 3 l 7 s s 4 s 2 o BINARYOUTPUTS PATENTEU Am; 5 I975 SHEET WFDAPDO o N m v m m BACKGROUND OF THEINVENTION This invention relates generally to encoding devices, and morespecifically relates to apparatus for converting the analog value of arotatable shaft to corresponding digital information for transmission toa utilization point.

Electric, gas, water, or similar meters are typically characterized by aplurality of rotatable shafts, which are so inter-related thatsuccessive shafts are angularly displaced on a basis or other ratio withrespect to its neighbor, whereby a direct decimal readout of the meteris enabled, by means of indicator hands which rotate with the severalshafts about dials on a face plate. In a typical power utilityinstallation for example, periodic reading of the meter is conducted byan individual who inspects the readings at each of the plurality ofdials associated with the several shafts, and thereby may record adirect decimal value.

Within recent years a considerable amount of inter est has beenevidenced in the concept of automating the readout function of thepolydecade meters, as described above. Among the reasons that may becited for such interest is a desire to reduce the cost of manualservicing, and the fact that the meters sought to be read are often inrelatively inaccessible places in homes, and at factories and otherindustrial installations. Moreover interest has centered in providing anautomated readout in such a form that the said readout may be directlytransmitted as, for example, by conventional transmission lines to theutility company or other provider of the services recorded on the meter.

In order to achieve the results indicated, numerous constructions havebeen provided, which digitally encode signals from the said meters inaccordance with the decimal readings present thereat. A principalproblem, however, with the bulk of proposed prior art systems has beenthat errors in the automated readouts can occur in several ways, each ofwhich may introduce intolerable results into the digitally transmittedinformation. In this connection it may firstly be noted that one sourceof such error lies in the binarycode itself, where a change from onedecimal number to a successive number may be represented by change atseveral of the corresponding binary digits. This introduces thepossibility of multiple points at which error can be made in theconversion process. In order to eliminate this possibility it has becomecommon to utilize in analog-to-digital conversion equipment, theso-called Gray code or reflected binary system. The advantage of thecited Gray code system is that successive integers differ from oneanother by only one digit. Under some circumstances, however, as willbecome further apparent hereinbelow, a simple reflected binary systemyet permits ambiguities in that when the binary 0 is represented by theabsence of a signal, it is not desirable to have a decimal symbol 0represented by binary 0000 since it cannot be distinguished from ano-signal condition.

In the type of meters to which the present invention appertains, afurther and highly significant source of error may occur as a givendecade approaches a whole number. For example, in a typical watt-hourmeter we may consider the ambiguity that may arise upon the dial pointerhand for the thousands reading approaching a whole number. As thishappens it will be evident that the adjacent hundreds dial pointerapproaches simultaneously 0. Suppose the thousands pointer thus reachesthe whole number 6 as the hundreds pointer is between the digits 9, and0. It will be evident that a manual observer reading the said dial platewould properly read the number as 5900. On the other hand, a straightdigital readout from the adjacent dials could erroneously indicate areading of 6900 a relatively enormous error. Basically, it will beevident that the manual decision process involved in obtaining a correctreading involves inspecting the lower decade in an ambiguous situation,and making a decision from the reading at the lower decade as to whatvalue should properly be assigned to the adjacent higher decade. Inother words, in the example cited, the observer having decided that thehundreds pointer is between 900 and 1000, then assigns a value of 5000to the adjacent thousands-decade pointer.

The possible sources of error as above described, can accordinglyintroduce intolerable results into a digitally encoded readout. In thepast, in order to eliminate the several possibilities cited, relativelycomplex and bulky electronic and/or optical means have been proposed foruse in conversion devices of the present type. Not only, however, havesuch proposed constructions tended tointroduce inordinate andunacceptable costs into said equipment, but moreover the consequent bulkof the proposed constructionshave been such as to not be readilyapplicable to the compact meters that are commonly employed in utilityand similar measuring applications: forexample, the manually read wheelsassociated with a typical power utility meter, may be the order ofone-half inch in diameter. In this type of com pact environment the use(as sometimes proposed) of numerous auxiliary tracks to removeambiguities of the type mentioned in the foregoing paragraphs becomeshighly impractical.

In copending application, Ser. No. 314,391, filed Dec. 12, 1972, now US.Pat. No. 3,846,788 for POLYDECADE DECIMAL TO DIGITAL EN- CODER, whichapplication is assigned to the assignee of the instant application, wedisclose encoder apparatus which eliminates many of the foregoingproblems. In accordance with that disclosure, a system is set forthutilizing a plurality of point light sources and paired, pointphoto-sensors, together with a plurality of encoder wheels, one of whichis associated with each successive decade shaft of the meter. Concentriclight transmitting tracks are present on each of the said encodingwheels, which tracks cooperate with the light source-sensor pairs, toprovide outputs at the sensors in accordance with the angular positionof the shaft and encoder wheels. Associated logic circuitry acts toeffect the reading decision where a borderline value is present at theleast significant digit being read on the meter. Upon this leastsignificant digit reading being determined, the said logic directsselection of the sensors utilized for reading successively higherdecades in accordance with the decision rendered at the LSD reading.While that system is therefore highly effective, for the purposes setforth, it yet remains relatively complex in utilizing a relatively largenumber of diodes or other sensors, and a fairly complex logic scheme inorder to resolve the ambiguities.

SUMMARY OF INVENTION In accordance with the principles of the presentinvention, the encoding wheel associated with each decade of apolydecade meter, is divided into sectors, which in general are ofnumber S, successive code wheels being coupled through a gear train witha reduction in ratio of n. The specific number S of sectors determinesthe number of bits of coding for a binary system, i.e., the minimumnumber of bits equals the integer value of the quantity log S.Accordingly, if 16 sectors are utilized as will representatively be thecase, 4 bits are required; where sectors are utilized, 4 bits arerequired; with eight sectors, 3 bits are utilized, etc. The rotationalpositions of each of the said encoding wheels are determined byconventional machinereading techniques as, for example, by opticallyexamining the four tracks of coding that may representatively be presentwhere 16 sectors are present around the periphery of a code wheel. Thesectors are read out in a cyclic Gray code, which is then converted foreach decade to a decimal number, corresponding to the specific sector,as for example, 0 through where 16 sectors are present. Ambiguitycorrection of the successive higher decades is then effected byexamining the higher decade in the case of any pair of adjacent decades,using its value to establish the possible range of the lower (i.e. finewheel); thereupon examining the fine (lower decade) wheel to determinewhether it falls in the said range, and thereupon adjusting by plus or-1 the read value of the corresponding coarse wheel (or allowing themeasured value to stand) in accordance with the measured fine wheelvalue relative to the said range. Ambuiguity correction is therebyeffected, by repeating this technique is serial fashion for thesuccessively higher decades. Means are present for further evaluatingthe total number of accumulated sectors that have passed a referencepoint in the case of LSD (least significant digit) wheel, and for thenscaling the sectors determined to be cumulatively present on each wheel,to decimal values.

BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammaticallyillustrated, by way of example, in the drawings appended hereto inwhich:

FIG. 1 is a schematic plan view of an encoding wheel of the typeutilized in the present invention; and

FIG. 2 is a schematic block diagram, showing the manner in which theprinciples of the invention may be employed in a decimally gearedsystem, utilizing a minimum number of binary bits to correct forambiguities.

DESCRIPTION OF PREFERRED EMBODIMENT In accordance with a preferredembodiment of the present invention, it may be assumed for purposes ofconcrete illustration, that each encoding wheel associated with a givendecade of a polydecade meter is provided with 16 pieshaped sectors,extending about the face of the encoding wheel. An encoding wheel 10 ofthis type is shown in FIG. 1, the wheel being utilizable for example, inapparatus such as that set forth in our copending application, Ser. No.314,391, previously referred to. As is further illustrated in the saidapplications, an encoding wheel 10 of this type rotates in coaxialfashion with the shaft defining a specific decade of the polydecademeter, and interacts with optical or electrical reading means which arecapable of examining the said wheel and determining the angular positionthereof. More specifically in the present invention, that which isrequired to be ascertained in which of the 16 sectors 12 proceedingabout the wheel overlie a reference line 14 at a given readout time.Typically four concentric tracks of coding may be provided about thesaid wheel, so that the machine reading means, may by examinationof thebits defined in each of the four tracks determine which specific sectoris overlying reference line 14, i.e. which sector 12 the sensors aredetecting atthat given time. The use of such readable indicia tracks todetermine angular position of a code wheel, is per se well-known.Reference may be had in this connection, for example, to US Pat. No.

3,262,108. For purposes of simplicity, only a portion 16 of such tracksis shown in the Figure. The number of indicia tracks utilized are suchin relationship to the number of sectors, as to enable an unambiguousoutput indicative of the sector being read. The coding utilized on theindicia tracks is preferably a reflected Gray code, since this insuresthat when a borderline situation exists the number read out of theencoders will be in error by at most 1 bit. It should also be recognizedin this connection that borderline situations of this type only occurwithin the resolution of the encoder, i.e. each encoding wheel ispositioned with a certain angular accuracy, and 1 bit errors only occurwhen the code wheel has a border over the light source (assuming that asensor-light source pair construction is in fact utilized to readout thebits, as is shown in the aforementioned Ser. No. 314,391 application).The numbers 18 seen to identify each sector 12 are of course atdifferent angular positions than the numbers 20 representing the decimaldivision of wheel 10.

In order to understand the nature of the ambiguity and error correctionachieved by the invention, we may consider that the encoding wheelsheretofor referred to are, in general, divided into sectors of number S,and the encoding wheels are coupled to a gear train with a reductionratio of n. It is assumed that all code wheels and gear ratios betweencode wheels are the same. The number of sectors determine the number ofbits of coding for a binary system, i.e. the minimum number of bits I.V.[log S], where the designation LV. refers to the integer value of thebracketed expression. Thus it is evident pursuant to this terminology,that where 16 sectors are present, 4 bits are appropriate for encoding;where 10 sectors are present, 4 bits are appropriate; where eightsectors are utilized, 3 bits are appropriate, etc.

Ambiguity correction insures that the corrected number is accurate tothe accuracy of the least significant digit (LSD) wheel, with aresolution of one sector of the least significant wheel, the leastsignificant wheel being the fastest wheel. The ambiguity correction,therefore, uses the position of the least significant wheel as thereference for all corrections. The general procedure is to accept theposition of the least significant wheel, and use itto correct the nextmost significant wheel. Once the second most significant wheel iscorrected, it in turn is used as a reference for correcting thethird'most significant wheel. This iterative process is repeated untilall wheels have been corrected. The procedure thus is such, that theambiguity correction can be considered'for purposes of analysis, tooccur between only two wheels, i.e. a fine wheel gfastest) used as areference, and a coarse wheel, i.e. the wheel to be corrected. 7

Continuing this analysis, on an assumed basis ofa single fine and coarsewheel, it may be assumed that the encoder apparatus is initiallypre-aligned such that there is a zero on all encoding wheels when theencoder reads zero, i.e. the border between the highest sector and thelowest value sector is in transition on all wheels. As the encoderrotates the number Np of sectors on the fine wheel passing the zeroreference, cause a certain number N of sectors to pass the zeroreference on the coarse. Since the code wheels are identical, it followsthat N N /n. It should be noted here that the number of sectors N arenot limited to the number of sectors on the wheel, i.e. if n 10, S 16,and N 12; therefore, Np 120 sectors, although the code wheel can in thisillustration only identify 16 different sectors. It should further benoted that when the fine wheel is on a sector border, that the coarsewheel is not necessarily on a border; e.g. if n 10, s 16 and N 16; thenN l.6.

The ambiguity correction begins by examining the coarse wheel and usingits observed" value to establish the range of N lf N/,,,,-,,,. isdefined as the minimum value that the fine wheel can have as calculatedfrom the coarse position, then N N, total completed revolutions of thefine wheel (in terms of sectors). The total number of revolutions of thefine wheel is the integer value of the expression {(N(' (n)/S} where Nis the measured valueof the coarse wheel. Said integer value beingenclosed in braces represents the preceding whole number since that forexample a value of 2.3 would have an integer value of 2. Therefore,

(Nr'm) (n) S and the maximum value the fine wheel can read is n N,.-|.v. s s N s N,-,,,+ l)-l.V.

This specifies the minimum and maximum values (Modulo S), that N canhave, if N is correct If N does not fall in this range, N is incorrect.

lf Np N 1 should be subtracted from N such that the correct coarse valueN(' is: N N l.

Similarly, if NF B N]-I I,' l should be added to Np, such that thecorrected coarse value becomes; N(' N -,,,+1. Thus the coarse wheel iscorrected. The next step to use the corrected coarse wheel as areference for the next most significant wheel, performing the cor- Tospecify the range where errors can occur and be corrected,- whether fromambiguities or alignment errors, it should be noted for ambiguitycorrection a necessary condition is that This can be seen by consideringa decade mechanical counter, continuously geared with 10:1 ratio, suchas a watt-hour register. If the number of sectors/wheels is 10,borderline ambiguities cannot be resolved, becaue they occursimultaneously on the low order decades.

The number of sectors of fine that is covered by one sector of coarseis:

(n), sectors of fine therefore, (s-n) sectors are available forambiguity correction in the fine wheel, or the allowable misalignment ofthe coarse is; s-n/n g c, error in sectors of coarse. This errorin.degrees becomes;

, 360 s n S n v dea.

360 360 (s-n) n s ns Ex.,

for n =10, r= l6 E C,1.,, 60 (360) 13.5 or, i 6.75 of coarse forn=l0,.r=20

10 C 360 18, or 1 9 Once all the wheels have been corrected, the processof converting the individual wheel readings into the equivalent totalnumber of sectors at the fine wheel can be accomplished. Once the totalnumber of sectors of fine is known, the number can be converted by anyscale factor desired. It should be appreciated that the total number offine sectors is not the sum of all different wheel values scaled by n,as the case for decade counters with 10 sectors. This is due to the factthat the sectors for the various wheels do not pass the boundariessynchronously and a fine wheel may have passed to a new sector withoutthe coarse wheel changing sectors. This in fact is generally the case.

nary data to mod 16 decimal. A representative table of The number ofaccumulated fine sectors in the (r-l) this type is set forth as Table Ihereinbelow:

wheel that were not accumulated on the r" wheel are:

D B A Sector Value o 0. 0V 0 nN rt 0 o 0 '1' 1 n [NW1 (nN, nN, l.V. S(S))] C,.. 0 0 l l I 2 0 0 1 ,0 3 Similarly, the next wheel contributes;I l g 0 1 0 1 6 l0 0 1 0 0 7 NF 1 1 o 0 s n'-*[N.-,-(nN,- .1.v. ())1=c.. 1 l e 0 l 9 1 1 l 1 I0 I 1 1 0 ll until the last wheel; 1 8 i l5 lO O 1 l4 1 0 0 0 N These numbers will represent the measured numbers S l(8)] from each decade:

N Number of sectors in units measured. The total amount of fine sectorsbeing; NT. Number of Sectors in tensmeasured.

N Number of sectors in hundreds measured. N Number of sectors inthousands measured. It is these four numbers that will be processed.

5 1 2. Ambiguity & Error Correction T Z, Ci A. Tens Decade i=0 1.Calculate possible range of N from N This value can be scaled by anydesired factor. After 2. If N falls in this range, accept N a N,scaling, the conversion is complete. rect value) It may be noted in theforegoing connection, that 3. If N is less than the lower bound,subtract 1 where 16 sectors are present, and n 10, the resolution from Ni.e.,

of the meter is one decimal digit in the units decade,

where the resolution of the code wheel is (1/16) (10) 40 l Correctedvalue of a decimal digit. Since the data is scaled to decimal, 4. If Nis equal to or greater than the upper bounthe actual angular errorcannot exceed one sector, ald, add 1 to N, though a decimal number willresult. Therefore, the

N,= l corrected value maximum error is: 10/16 0.63

Assuming that 16 sectors are actually present in the B. Hundreds Decadeencoding wheels of the invention, we may summarize l. Calculate possiblerange of N from N N ro N,,,,,+1 10 l()N,, l.V. I6 s N, l()(N,, l-l)l.V.16

the four main steps required in providing a decimal 2. [f N, falls inthis range, accept N readout as follows: N N

1. conversion from each of he c clic od t y Gray C e 3. lfN, falls belowthe lower bound, subtract 1 from numbers in each decade to a decimalnumber ranging from 0 to l5; 2. ambiguity correction of the three higherdecades,

NH", i.e.,

' N N l corrected value tens, hundreds and thousands; 4. If N, is equalto or greater than the upper bound, 3. evaluation of the total number ofaccumulated add 1 to N fine sectors, 8-,- 4. scaling the above sectorsto decimal values. lzcor'rected value In effecting (l) as above setforth, a look-up table is C. Thousands Decade effectively required toconvert the incoming Gray bi- 1. Calculate possible range of N from H 2.If N falls in the range, accept m,

th NM,"

The above assumes no alignment errors, but since an alignment error ofup to 0.3 sectors can occur in all but the least significant decade,which is assumed error, a possible set of numbers could be:

3. If N falls below the lower bound, subtract one from N N N l correctedvalue 4.:If N is equal to or greater than the upper bound,

add one to N N1}. N l corrected value This completes the ambiguity anderror correction.

3. Evaluation of total number of fine sectors a; Thousands decade b.Hundreds decade c. Tens decade d. Units Decade i (I OH F LV.

e. Sum of all fine sectors" S7 C C l Cm 4. Scaling to Decimal Decimalvalue F5 This completes the entire conversion.

This section gives some numerical examples of possible conversions:

EXAMPLE 1 Assume the number to be converted is: 6299.000

Gray Binary Word portion to be encoded Units in Sectors 1440 l 0 0 lTens in Sectors 1584 l O 0 0 Hundreds in Sectors 4.784 0 l l 0 Thousandsin Sectors 10.0784

Gray Binary Word Units in Sectors M2 l 0 0 l Tens in Sectors I 1601 0 0O 0 0 Hundreds in Sectors 5.03 0 l l 1 Thousands in Sectors 9.91 l 1 0 lThe data entering the interface is:

Units 1 0 0 l Tens 0 0 0 0 Hundreds 01 l l Thousands l 10'l' This datagets converted via the look-up to:

Ambiguity Correction Tens Decade Therefore, the range is (in Modulo 16)l accept +1 Since, N m falls below the range, 1 must be subtracted fromN Ambiguity correction for Hundreds Decade 3(l6) s N, 60-3 16)Therefore, the range is:

N,,,=9 +1 =10 v This completes the ambiguity and error correction, whereIt is interesting to note that the sector values are those that appearedbefore the errors were introduced.

Tens Decade l (l (40-32)) l0 (IS-'8) 70 70 Units Decade S /16) DecimalNumber Decimal number 10078 (10/16) 6298.75 which is correct to within 1l sector of the least significant decade.

EXAMPLE 2 Convert the number 9999.9

which gets converted via the look-up table to:

Units Tcns l5 Hundreds 0 Thousands 15 In FIG. 2 a system in accordancewith the invention is shown, based upon a 4 bit binary code (i.e. 4 bitsper encoding wheel), where successive wheels are geared on a l0:l ratio.Readout means 30 and 32 are respectively associated with a course and afine encoding wheel as have been discussed in the foregoing analysis.This is to'say that means 30 and 32 are typically as sociated withsuccessive decades in a polydecade meter. Four parallel outputs areprovided from eachof means 30 and 32, as respectively shown at referencenumerals 34 and 36. It is assumed for purposes of this analysis that theoutputs 34 and 36 from each of the means 30 and 32 are already convertedfrom Gray to ordinary binary form. The outputs 36 from the fine encodingwheel are provided to correction analysis logic 38 and also are part ofoutputs 48. The outputs 34 from means 30 are initially re-weighted atscaling means 40 so as to be binarily related to the outputs from means32. This may be effected by simple multiplication by the binary factorl0l. The outputs 37 from scaling means 40 are in turn provided tocorrection analysis logic 38, which utilizing conventional logicelements perform the ambiguity analysis set forth above. An output isprovided in lines 42 from correction analysis logic 38 to revolutionscorrection logic 44, which directs the addition or subtraction of one,or the acceptance of the number of revolut'ions indicated; by the fouroutput lines 46 from scaling means 40. The corrected readings in binaryare now present at all of the output lines 48, which may then beprovided to scaling means, to conventional binary to BCD conversionmeans, etc., so as to yield a decimal readout.

While the present invention has been particularly set forth in terms ofspecific embodiments thereof, it will be understood that numerousvariations upon the invention are now enabled to those skilled in theart, which variations yet reside within the scope of the presentteaching. Accordingly, the invention is to be broadly construed, andlimited only by the scope and spirit of the claims now appended hereto.

We claim:

1. Encoding apparatus for providing unambiguous data outputs frompolydecade meters of the type including a plurlity of successivedecades, each decade including a rotatable shaft for a dial indicatorassociated therewith, successive shaft rotations being related by afixed gear ratio n therebetween, comprising in combination:

Actual Assumcd Mcasurcd Gray Sectors Error in Sectors Sectors BinaryWord Units in Sectors 15.84 +.l6 0 0 0 0 Tens in Sectors l5.984 0 15 l 00 Hundreds in Scctors l5.9984 +.l 0 (l 0 0 0 Thousands in Sectorsl5.99984 0 15 l O O 0 Entering the interface are the four gray binarywords Units 0 0 0 0 Tens l 0 0 0 Hundreds 0 0 0 0 Thousands l O (l 0 aplurality of encoding wheels, at least one said wheel 13 ity of sectorsextending about said wheel; machine readable indicia on said wheel fordetermining which of said sectors is at an angular reference position;

means for reading said indicia at the wheels associated with arespectively higher and lower order decade, to provide measureddeterminations of the rotational positions of said wheels in terms ofsaid sectors;

means for establishing the possible rotational range of said lower orderdecade wheel from said measured value of said higher order wheel;

means for comparing the measured rotational position of said lower orderwheel with said determined range to generate an adjusting signal; and

means for adjusting upwardly, downwardly or leaving unchanged themeasured value of said higher decade wheel, in accordance with saiddetermination of whether said lower decade wheel falls within saidrange.

2. Apparatus in accordance with claim 1, wherein at least said wheelassociated with said lower order decade is divided into s of saidsectors, and wherein the ratio s/n is greater than 1.

3. Encoder apparatus in accordance with claim 2, wherein said sectorsare initially read out in a cyclic reflected Gray code.

4. Apparatus in accordance with claim 3, wherein said read-out cyclicGray code is converted to a decimal number corresponding to the sectorsprior to establishing said range and evaluating the relationship ofadjacent decades to said determined range.

5. Apparatus in accordance with claim 4, further including means fordetermining the total number of accumulated sectors which have passedsaid reference position at said lower order decade wheel, and forscaling the accumulated secors to provide a decimal output for saidencoding apparatus.

6. Apparatus in accordance with claim 5, wherein said wheels areprovided with concentric indicia tracks about the face thereof, ofsufficient number in relationship to the number of sectors to provide anunambigu ous bit output indicative of the sectors being read.

7. Apparatus in accordance with claim 6, wherein said encoding wheelsare divided into sixteen said sectors, said decades being four innumber.

1. Encoding apparatus for providing unambiguous data outputs frompolydecade meters of the type including a plurlity of successivedecades, each decade including a rotatable shaft for a dial indicatorassociated therewith, successive shaft rotations being related by afixed gear ratio n therebetween, comprising in combination: a pluralityof encoding wheels, at least one said wheel being coaxially mounted forrotation with the rotatable shaft associated with each decade of saidpolydecade meter; each said encoding wheel being divided into aplurality of sectors extending about said wheel; machine readableindicia on said wheel for determining which of said sectors is at anangular reference position; means for reading said indicia at the wheelsassociated with a respectively higher and lower order decade, to providemeasured determinations of the rotational positions of said wheels interms of said sectors; means for establishing the possible rotationalrange of said lower order decade wheel from said measured value of saidhigher order wheel; means for comparing the measured rotational positionof said lower order wheel with said determined range to generate anadjusting signal; and means for adjusting upwardly, downwardly orleaving unchanged the measured value of said higher decade wheel, inaccordance with said determination of whether said lower decade wheelfalls within said range.
 2. Apparatus in accordance with claim 1,wherein at least said wheel associated with said lower order decade isdivided into s of said sectors, and wherein the ratio s/n is greaterthan
 1. 3. Encoder apparatus in accordance with claim 2, wherein saidsectors are initially read out in a cyclic reflected Gray code. 4.Apparatus in accordance with claim 3, wherein said read-out cyclic Graycode is converted to a decimal number corresponding to the sectors priorto establishing said range and evaluating the relationship of adjacentdecades to said determined range.
 5. Apparatus in accordance with claim4, further including means for determining the total number ofaccumulated sectors which have passed said reference position at saidlower order decade wheel, and for scaling the accumulated secors toprovide a decimal output for said encoding apparatus.
 6. Apparatus inaccordance with claim 5, wherein said wheels are provided withconcentric indicia tracks about the face thereof, of sufficient numberin relationship to the number of sectors to provide an unambiguous bitoutput indicative of the sectors being read.
 7. Apparatus in accordancewith claim 6, wherein said encoding wheels are divided into sixteen saidsectors, said decades being four in number.